I bought these to replace a worn out dog nail grinder head made by Casfuy. They fit and work well. I don't know how long they will last but I only use it on one small dog and will replace as needed. It is nice keeping extras on hand. I do use a nail trimmer but use the grinder as final touch up and to smooth closer to the quick. We have had no accidents with this technique. The vet tech continually cut into the dog's quick, so I learned through much patience and now do a better job than they ever did. The key is special treats, patience and break up the session if you have to. If you are not afraid to work with your dog, you will be happy you learned to use one of these nail grinders with replaceable grinding heads.